Scanning head

Abstract

A scanning head (12) for a surface measuring machine has a probe tip (30), which is supported by a probe tip support lever (18) so that it can be deflected perpendicularly to the reference surface (82). Incorporated between the probe tip (30) and a rigid section of the probe tip support lever (18) is a force sensor (34), whereof the output signal serves as an actual value of a control circuit (56 to 60), which controls a magnetic servo motor (44, 46), which exerts a variable additional force, to be added to the force of a tension spring (42), on the probe tip support lever (18), the whole so that the contact pressure of the probe tip (30) is kept constant irrespective of the surface contour.

I claim: 
     
       1. A scanning head for a machine for measuring the micro-surface contouor of work-pieces which includes a housing (14), a rigid probe tip support (18) mounted (16) to move on the housing (14) and which supports a fine probe tip (30) means (42 to 46) for the resilient biasing of the probe tip (30) against the work-piece surface (10) and a position indicator (50) cooperating with the probe tip support (18), characterized in that a force sensor (34; 50, 86, 88) is provided which measures the force acting on the probe tip (30); and included in the biasing means is a controllable servo motor (44, 46) acting on the probe tip support (18), the output force of which is adjusted (56 to 60) to a constant output signal of the force sensor (34; 50, 86, 88), the probe tip (30) on the probe tip support (18) being shiftable perpendicularly to the reference surface (82) and being supported by way of the force sensor (34) on the probe tip support (18). 
     
     
       2. Scanning head according to claim 1, the probe tip support being a support lever (18) extending substantially parallel to the work-piece surface (10), characterised in that the probe tip (30) is located on a leaf spring (26) extending in parallel below the support lever (18). 
     
     
       3. Scanning head according to claim 2, characterised in that the force sensor (34) is seated with resilient biasing between the probe tip (30) and the support lever (18). 
     
     
       4. Scanning head according to one claim 1, characterised in that the force sensor (34) comprises a solid state sensor. 
     
     
       5. Scanning head according to claim 1, characterised in that the force sensor (34) is connected by way of a lead (38) of low resistance to bending, which even when the probe tip support (18) is fully extended, is pre-deflected from the neutral axis, to a lead (40) integral with the housing. 
     
     
       6. Scanning head according to claim 1, characterised in that the force sensor (50, 86, 88) comprises a position indicator (50) preferably cooperating with the probe tip support (80) and a double differentiating stage (86) connected thereto. 
     
     
       7. Scanning head according to claim 1, characterised in that the position indicator (50) is a position indicator operating using the Hall effect. 
     
     
       8. Scanning head according to claim 1, characterised by a force/displacement characteristic circuit (74) receiving the output signal of the force sensor (34; 50, 86, 88) and by an adder (78), which receives the output signal of the latter and the output signal of the position indicator (50) cooperating with the probe tip support (18). 
     
     
       9. Scanning head according to claim 8, characterised in that the force/displacement characteristic circuit (74) is exchangeable or contains a plurality of different force/displacement characteristics, of which respectively one can be activated by a selection unit (76). 
     
     
       10. Scanning head according to claim 1, characterised in that the servo motor comprises a permanent magnet (44) connected to the probe tip support (18) and a magnet coil (46) supported by the housing (14). 
     
     
       11. Scanning head according to claim 1, characterised by a reference value switching circuit (62 to 66), which switches over the reference value signal for the servo motor control circuit (56 to 60) between different values. 
     
     
       12. Scanning head according to claim 1, characterised in that the probe tip (30) is symmetrical to its central plane which is perpendicular to the scanning direction, preferably is rotationally symmetrical and its location on the probe tip support (18) as well as the location and mounting (16) of the probe tip support (18) on the housing (14) are chosen so that the relative movement between the probe tip (30) and work-piece surface (10) takes place in the positive and negative scanning direction under the same conditions.